First of all, you should define what a useful altcoin is in your opinion
The thing is, everyone has a other definition of "useful" and therefore everyone is investing in different altcoins. it is very subjective decision.
I'll try to answer this question although I'm not the OP.
"Useful" altcoins are cryptocurrencies that have one or more of these three characteristics:
- Coins with an unique feature (or are the first movers) with direct benefits for the users. Example: NXT, with its asset exchange; BitShares, with market-pegged assets; MaidSafe / Storj, Darkcoin/Dash (anonymity), XRP, etc.
- Experimental coins which explore a new approach to the standard features of a cryptocurrency, like new consensus algorithms. They can be considered useful if their approach has some potential advantage to other concepts. Examples: Peercoin (first Proof-of-Stake coin), Slimcoin (first Proof-of-burn coin), NEM (Proof of Importance), Timekoin.
- Coins which are actively used in real economics (buying and selling goods and services, donations ...) because of their large community, although they don't have a unique technical feature. Example: LTC and Doge.
Most of these coins are doing quite well (Timekoin and Slimcoin are exceptions). But sometimes the pumps of simple clonecoins overshadow them. That is probably what the OP means.
What we perhaps need is an alternative to Coinmarketcap focused at the long-term.
